Cotton is used in many products due to its many desirable characteristics. For example, cotton is used in absorbent products due to its high absorbency and is used in wearing apparel due in part to its many comfort properties (such as, for example, the natural moisture regain of cotton fibers and the moisture vapor transport and air permeability/breathability of fabrics made from cotton). However, some of the properties of cotton make its use undesirable in certain products.
For example, cotton has not traditionally been preferred for use in “recreational performance apparel” primarily due to its high absorbency. “Recreational performance apparel,” as defined herein, is any apparel that is recommended for use during activities that may involve perspiration. For any fabric to perform in such garments, the moisture must be wicked “away from the skin” (i.e., the moisture must be transported away from the skin to the outside of the garment where it is dispersed). The moisture must in fact be absorbed by the fabric (i.e., pass through the fabric in the Z direction as well as spread or wick in the X and Y directions) whereby the outer layer or outside of the garment becomes wet and evaporation can occur. The same wicking effect must occur in a layered clothing system when perspiration occurs, as the liquid moisture must pass from an inside layer to an intermediate or outer layer whereby it eventually can evaporate.
The high absorbency of cotton translates into a variety of problems when used in garments where the consumer undertakes activities generating moderate or heavy perspiration for prolonged periods. These problems are that the garment gets too wet and heavy, sags due to the water weight, takes too long to dry, and sticks to the skin. Since skin is hydrophilic and the inside of the cotton fabric is hydrophilic, there is an interfacial/surface tension which forms at the skin/perspiration interface and at the fiber/perspiration interface. The interfacial tension combined with the surface tension of the water or perspiration cause the garment to stick to the skin when wet. This leads to discomfort and restricts the freedom of movement, which can be especially bad during athletic activity. Wet cotton fabrics can also make the wearer feel cold, especially after exercise or when moving into an air conditioned environment. The slow drying may allow more time for odors to build up due to bacterial action on the perspiration.
An alternative to using cotton in recreational performance apparel is to use hydrophobic synthetic fibers in the apparel. A variety of treatment chemistries are commercially available that can be used to produce wicking of liquid moisture in normally hydrophobic thermoplastic synthetic garments. (See, e.g., Reference paper on wicking finishes by Hodgson Chemical given at the AATCC Functional Finishes and High Performance Textile Symposium, University Hilton, Charlotte, N.C., Jan. 27–Jan. 28, 2000). The wicking finishes do not penetrate into typical hydrophobic synthetic fibers such as polyester. They are very hydrophilic and some can absorb up to 200 times their weight in water. These treatments do allow wicking of liquid moisture in otherwise non-absorbing fabrics. Garments made from these treated fabrics have become popular, as evidenced by products such as very thin polyester T shirts with a wicking finish.
The disadvantages of products like polyester shirts with wicking finishes are that they do not provide the same level of comfort to the wearer during periods of non-exertion as cotton garments. Polyester absorbs almost no water within the fiber and tends to feel clammy when relatively low levels of liquid moisture are present, because the moisture is present on the surface of the fibers. In addition, many synthetic garments suffer from odor retention problems.
There are also treatment chemistries available that are used to provide water repellency or other hydrophobic properties to cotton and/or other hydrophilic fibers. These include, for example, waxes, silicones, and fluorochemicals. Such chemicals are typically applied by padding, the goal of which is to saturate and distribute the chemical finishes uniformly throughout the fabric in all directions. Tightly woven cotton fabrics treated with such compounds can be used for raincoats or awnings. However, when used for recreational performance apparel, perspiration is not wicked away, but rather collects between the skin and the fabric, which can be highly uncomfortable to the wearer.
Synthetic fabrics are also typically preferred over cotton fabrics for certain recreational performance apparel applications because most cotton garments (such as t-shirts and running shorts) that are used for certain athletic activities are relatively thick and heavy (i.e., the fabrics have a high area density) compared to many of their synthetic counterparts. The cotton fabrics used in these garments are thicker than their synthetic counterparts because of the physical properties of the fibers, filaments, and the yarns used to produce them. The increased thickness of the cotton garments further aggravates the moisture management issues because thicker fabrics absorb more moisture (i.e., have a higher absorbent capacity), get heavier, and take longer to dry. Thicker fabrics, with other variables held constant, have more internal capillary spaces which hold liquid than do thinner fabrics.
Cotton has also not been preferred in some absorbent products that are worn next to the skin. For example, cotton has not been preferred in the topsheets of adult and baby diapers and sanitary napkins. (The topsheet is the part of an absorbent disposable diaper or sanitary napkin which touches the skin of the user and which is typically a nonwoven fabric.) Urine or menstrual fluid must pass through the topsheet and into an absorbent core where it is trapped. In order to maximize the comfort of the user of such a product, it is desirable to maximize the wicking of liquid in the Z direction (i.e., the direction normal to the plane of the fabric) and away from the skin. The ideal scenario is for the topsheet to stay dry.
Polypropylene nonwovens have established themselves as the most common topsheet material. Although polypropylene is a relatively inexpensive fiber, it is not widely used in general wearing apparel that is to be worn next to the skin. This is because polypropylene is not as comfortable as cotton, because polypropylene is not readily dyeable, and because polypropylene adsorbs and holds odors. Furthermore, polypropylene may tend to exacerbate skin irritation. (See, e.g., Baby Diapers in Y2K—the challenge for the nonwovens industry continues, Nonwoven Markets, Oct. 9, 2000, Miller Freeman Inc.)
Disposable diapers, sanitary napkins, and any absorbent products that use polypropylene next to the skin are lacking in basic comfort properties in comparison to products that have cotton next to the skin. In the dry state (i.e., prior to urination during use), a topsheet made from regular bleached cotton fiber would benefit the wearer by providing the many comfort properties of cotton. However, a topsheet made of 100% regular bleached cotton would tend to hold too much urine (or menstrual fluid) next to the skin.
It would be advantageous to provide products prepared from cotton or other cellulosic materials which have reduced absorbent capacity but include wicking properties. The present invention provides such products as well as methods of manufacturing such products.